1. Field of the Invention
This invention relates to a dispersion plating method which can be used in the production of electro grinder, for example in such a way that abrasive grains of a grain size larger than 10 .mu.m are made into a state of eutectoid in a metal matrix to produce electro grinders.
2. Description of Related Art
FIG. 1 shows a sectional view of electro diamond grinder which was presented in "Metal Surface Technique" published by the Metal Surface Technique Association (Vol. 33, No. 6, P. 285, 1982). This figure shows that diamond abrasive grains 31 are buried inside a metal matrix 33 which is formed on an object to be plated 32, and the diamond abrasive grains are made adhering to the surface so that they may not come out from the position. It has been reported that if diamond abrasive grains 31 are buried inside the metal matrix 33 to a degree of 65% of the diameter, those diamond abrasive grains 31 can be retained in the matrix most efficiently so that they may not come out of the position. It is also reported that it results in the highest level of grinding efficiency.
Usually abrasive grains from a small size of scores of tens .mu.m to larger than 100 .mu.m are used. Abrasive grains of these sizes, however, may not float and accordingly precipitate in plating liquid although it may depend on a level of specific gravity. In order to avoid the precipitation of abrasive grains in the plating liquid and make these grains buried in the metal matrix, abrasive grains must be held in a state of adhering over the surface of an object to be plated until the abrasive grains are buried.
Usually, electro grinders are produced in a two-stage process including the stage of adhesion plating and that of salvage plating. Adhering methods include a sedimentation adhering method and a package adhering method.
FIG. 2 shows a conceptual scheme of an eutectoid method of abrasive grains based on the conventional sedimentation adhering method, which was presented in "Composite Plating" published by a newspaper--The Nikkan Kogyo (Co-author: Hidehiko Enomoto, P. 108, Aug. 30, 1989). In this method, abrasive grains 31 are stirred and dispersed in the plating liquid. As a result, abrasive grains 31 precipitate over the surface of object to be plated 32 which is placed at the bottom of the container of the plating liquid. (See FIG. 2(a).) After the above-mentioned process, stirring is stopped and plating follows. Abrasive grains 31 which cover the surface of object to be plated 32 are made in a state of adhering to the surface slightly. (See FIG. 2(b).) After dismantling an extra amount of abrasive grains 31 which cover the object to be plated 32, plating is made again over the surface of the object in the plating liquid to increase the thickness of plating in such a condition that abrasive grains 31 are not dispersed in the plating liquid. In this way, abrasive grains 31 which are in an adhering state are buried inside the metal matrix 32. (See FIG. 2(c).)
FIG. 3 shows a conceptual scheme of an eutectoid method of abrasive grains based on the conventional package adhering method, which was presented in "Composite Plating" mentioned above. In this method, abrasive grains 31 are placed in a small bag 34 of a predetermined size. (See FIG. 3(a).) This bag 34 is put into the plating liquid 35. Then an object to be plated 32 is placed in the bag 34, and the abrasive grains 31 are made into a state of contacting the surface of object to be plated 32 evenly. Then plating is conducted in a minimal level, whereby abrasive grains 31 adhere to the surface. (See FIG. 3(b).)
In conventional electro grinder manufacturing method, sedimentation adhering process is most popularly employed. This method holds such a merit that it is possible to make abrasive grains 31 adhere over the surface of object to be plated 32 evenly. In addition, it is especially suitable for providing just one layer of adhering abrasive grains 31.
The existing dispersion plating method is conducted in the way mentioned above. In this method, sedimentation adhering is made mainly by making use of gravity of abrasive grains 31. Accordingly, plating can be made effectively if the surface of object to be flat. However, if the surface of object to be plated is of curving or complicated shape, abrasive grains 31 will adhere only to the flat area. It is accordingly necessary to move the surface of object to be plated gradually in the horizontal direction until it becomes in such a position that abrasive grains 31 fall onto the surface of object to be plated constantly. In addition, plating can be made not only over the area in which abrasive grains 31 adhere to the surface but also the area in which the plating liquid contact the surface. For example, in case of repeatedly conducting dispersion plating, the top level of abrasive grains 31 on a flat object to be plated 32 shown in FIG. 4(a) becomes increasingly higher in proportion to the frequency of dispersion plating . As a result, the height of abrasive grains 31 adhering over the surface of object to be plated 32 shown in FIG. 4(b) which holds a cylindrical shape may become uneven. This results in such a problem as eccentric dispersion over the object to be plated as a whole. It is, accordingly, necessary that while plating is conducted over the surface areas to which abrasive grains 31 adhere, other areas should be kept masked. As a result, in case of an object to be plated 32 which holds a complicated shape, there exists such a problem that many kinds of meticulous work is required for plating.
In addition, there exist such problems in the conventional dispersion plating method that it is impossible to control the dispersion of abrasive grains evenly, and that since the level of dispersion of abrasive grains is excessively high in general, abrasion tolls manufactured by the conventional method cause dulling easily if certain types of abraded materials are used.